Active grill shutters are being introduced in newer cars in order to meet stricter fuel economy standards. In operation, the active grill shutters are automatically closed to block air flow through the cooling system when cooling is not needed. In the closed position the active grill shutters help improve aerodynamics by reducing drag with the greatest benefit achieved at higher motor vehicle speeds. At other times, the active grill shutters are opened when necessary to reduce engine under hood temperatures. The active grill shutter (AGS) system is also used to control coolant temperatures, HVAC performance and exhaust emissions depending on the speed of the motor vehicle. During normal operation, the grill shutters are fully opened when the engine is off. When starting the engine from cold, the grill shutters are closed for as long as possible to help reach the most efficient engine operating temperatures more quickly. This helps reduce fuel consumption and emissions.
AGS systems typically incorporate an electronic control unit (ECU) or controller and AGS sensors such as Hall effect sensors which provide information with respect to the current position of the grill shutters back to the controller. Typically the AGS sensors are self-calibrating when the motor vehicle is first powered up.
There are many failure modes associated with an AGS system. The grill shutters could be stuck in position and the sensors could still be functional. The mechanical linkages for operating the grill shutters may become damaged over time. The DC shutter drive motor may function properly but without a load should the linkage break. Still further, the Hall effect sensors may become damaged or become contaminated from the environment in a manner that prevents their normal function. In this situation, the controller is not provided with data from the sensors that establishes the current position of the grill shutters.
While it is possible to infer that the grill shutters are in the closed position from a rising engine temperature, in cool climates that is not necessarily true. Also, in hybrid electric vehicles (HEVs), the vehicle may be driven in pure electric mode (EV mode) and the engine temperature may not change. Further, if the AGS system is stuck in the open position while driving in EV mode, there will be additional aerodynamic drag on the vehicle. Ideally, the AGS system should be closed when driving in EV mode when the combustion engine is cold and not operating. This document relates to a new and improved method and system that performs rationality testing of the AGS system to determine if the AGS sensors are rational and properly operating or if the grill shutters are mechanically stuck or not moving for this or any other reason such as a broken linkage. Advantageously, the novel method and system validate shutter movement and infer shutter position based upon (a) stall current of the shutter driver motor and (b) current drawn by the traction motor of the HEV.